resen

from Easton's 1897 Bible Dictionary
Resen
head of the stream; bridle, one of Nimrod's cities (Gen. 10:12),
"between Nineveh and Calah." It has been supposed that the four
cities named in this verse were afterwards combined into one
under the name of Nineveh (q.v.). Resen was on the east side of
the Tigris. It is probably identified with the mound of ruins
called Karamless.
    
from Hitchcock's Bible Names Dictionary (late 1800's)
Resen, a bridle or bit
    

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